What was done
Virgin Japanese beetles (Popillia japonica Newman) were collected immediately upon their emergence from the same area of a park in Urbana, Illinois (USA), where as larvae they had "fed on the same grass species and experienced the same weather conditions," after which they were fed soybean (Glycine max L.) leaves that had been grown at the nearby SoyFACE facility in either ambient-CO2 air (~370 ppm CO2) or CO2-enriched air (~550 ppm CO2) for the duration of their adult lives, during which period several aspects of their physiology and behavior were monitored and analyzed.

What was learned
O'Neill et al. discovered that the lifespan of the Japanese beetles "was prolonged by 8-25% when fed foliage developed under elevated CO2," and that "females consuming elevated CO2 foliage laid approximately twice as many eggs as females fed foliage grown under ambient conditions."

What it means
The four researchers state that the "increased longevity and fecundity of P. japonica may contribute to greater damage by this herbivore as the concentration of CO2 in the atmosphere continues to rise." On the other hand, they say that "the increase in fecundity of P. japonica fed high-CO2 foliage may not necessarily contribute directly to greater population size and herbivore damage, because increased egg production by P. japonica in elevated CO2 seems to have come at the cost of reduced egg weight, potentially leading to decreased juvenile survivorship."

Although they opine that the potential reduction in juvenile survivorship "is unlikely to be large," it remains to be demonstrated what the ultimate outcome of the CO2-induced impacts on the several interacting phenomena they studied will turn out to be in the longer term and in the real world. In addition, it remains to be seen to what degree similar phenomena occur in the lives of other species of fauna, including those that are not looked upon as pests. Hence, there are likely to be multiple positive and negative consequences (from the human viewpoint) of this suite of life-trait phenomena as the air's CO2 content continues to rise, and as the fecundity and longevity of the biosphere's many lifeforms are potentially significantly enhanced.